1. Field of Invention
This invention relates to a method for separating and recovering the components from materials or articles formed from multilayer plastics. More particularly, this invention relates to a process of separating and recovering at least two desired components of articles formed of co-extruded multilayer plastics.
2. Description of the Art
Due to the large number of articles manufactured from various plastics, discarded plastics have become a large source of waste materials which need to be placed in landfills. Some of the waste plastics are difficult to degrade and possibly hazardous to the environment. Thus, recycling and reclaiming discarded waste plastics has become important in controlling pollution and preserving the environment.
Numerous methods have been developed for separating waste plastic materials. Generally, plastic waste materials can be separated into the desired components which make up the material by various flotation processes. U.S. Patent No. 3,925,200 generally discloses such a process. Although these well known flotation methods are quite effective for plastics having different specific gravities, they are ineffective for multilayer plastics, plastics having similar density ranges, or plastics that have been co-extruded.
Zielinski discloses a method for the separation and recovery of thermoplastic materials containing contaminants in U.S. Pat. No. 5,061,735. In this process, the thermoplastic material which is to be recovered is simultaneously heated and agitated along with a contaminant which could possibly be another thermoplastic material. The mixture is heated to a temperature at which the desired thermoplastic will adhere to itself, but the contaminant will not become tacky. The impacting thermoplastic particles agglomerate, while the contaminant particles do not adhere to other contaminant particles or to the agglomerating thermoplastic particles. The resulting mixture is then passed through a series of screens to separate the larger agglomerated thermoplastic particles from the smaller non-agglomerated contaminant particles.
Tomaszek, in U.S. Pat. No. 4,728,045 discloses a method for reclaiming resin materials from scrap articles formed of two bonded plastic components. The bonded material comprises a first low density resin component such as polyethylene and a second high density component, for example, polyethylene terephthalate. In separating such a bonded plastic, Tomaszek first granulates the scrap articles. Using air separation, Tomaszek removes any paper and film forming the labels from the ground particles. The lighter particles, polyethylene particles, are then separated from the heavier scrap particles using a flotation method. The heavier scrap particles are then vigorously washed in a hot aqueous medium to disrupt the bonds between the two resins in the particles. These particles are then washed and flotation separated. The heavy particles are removed, dried and re-used. The low density scrap particles from the second flotation stage are returned to the first flotation stage and the procedure is repeated. The Tomaszek method is quite ineffective in the separation of multilayer plastics, in particular those that have been co-extruded. Tomaszek also requires reiteration of laborious steps to obtain any separation of the constituent particles from the bonded material.
U.S. Pat. No. 4,199,109 to Wanatabe discloses a continuous flow operation for recovering the constituents of laminated articles. This method comprises the steps of heating multilayer plastic particles in the range of 80.degree. to 200.degree. Centigrade. After the separate heating step, the heated articles are then crushed by means of shearing, impact or tearing forces to peel the layers of the plastic articles into small pieces of the constituent resins. The small pieces are then separated into separate components, using either a flotation method, air current separation method or a separation method based upon differences of the dielectric constant or resistance of the constituents. The Wanatabe method also utilizes many steps to separate multilayer plastics.
Although these methods are useful, there exists a need for easy, efficient and inexpensive separation of articles or materials made from multilayer plastics into the different plastics which are part of the multilayer.
Accordingly, a primary objective of the invention is to both effectively and efficiently separate and segregate at least two of the components of the multilayer plastic.
Another object of the invention is to easily and economically separate and reclaim at least two of the constituents of the multilayer plastic.
Yet another object of the invention is to reclaim the constituents of co-extruded multilayer plastics so that they can be efficiently reprocessed or reused.